Method and apparatus for controlling storage batteries



Oct. 9, 1934. O. BENSON 1,975,892

METHOD AND APPARATUS FOR CONTROLLING STORAGE BATTERIES Filed-March 1 934l a rear METHQDD AND APPARATUS LING @scar Benson, ivatemown !-iplication March *3, i934, Neri l i i i6 @lahns. (Cl. Hi -El i) Thepresent invention relates to methods and In the customary direct currentfeeder system, apparatus for controlling the float charge of a batteryshown at in 2 and consisting of series connected storage batteries, alarge number of series connected cells is con- In direct currentdistribution systems which nected across the station bus 6 by leads 8.In employ Storage batteries fl a n 011 the- 115 order to maintain thefloat current fairly con- 6 is customary to supply to the batteries aconstant, regardless of variations in the bus voltage, tinuous floatcharge to maintain them in fully a set of end cells 19 is adapted to beselectively charged condition in readiness for emergency cut intoservice by means of the end cell switch use. Such batteries ordinarilycomprise series 120i" any suitable form. 19 connected individual cellsin sufficient number to The cells are of the form indicated in Fig. i,'55 give the required line voltage of the system. Oweach comprising atani: l4 and sets of negative ing to natural deterioration, cells arebeing con= and positive plates 16 and 18 respectively, each tinuallyreplaced and as a consequence, a comp ate having S 29 Testing n pp 22 0fplete battery may be made u of c ll f widely glass or a suitableinsulating material. The different ages. The float charge is required tocells are permanently connected in series by a overcome the local actionwhich tends to take bridge or bus 24 burned to the positive platesplacecontinuously in any lead cell and since the Of O e ell a thenegative P a o he new? local action increases with the age of theplates, adjacent cell. the charge urr nt m t b im meg; t 3, value Theapparatus described is common to suincient to keep the oldest cellsincondition. l yp f dir ct current systems with floating '5 Owing to theseries connection, the same float Storage batteries- In Order to p m Cool charge current normally flows through all the charging of thediiierent cellsin accordance with cells. For newer and more efiicientcells in which $11611 the newer d e ic t l s are the local action issmall as compared with that pl'fivided With adjustable shunts indicatedgener- 25 of the less emcient cells, the maximurn charge lly at as. No prticular form or hunt is rctill current is not necessary and in fact ithas deleil except that it Should be Of a material w terious efiects inprematurely ageing such cells. affected by the fumes the atte y room andto The object of the present invention is to provide this end a carbonpile resistor is pi cfit- A a method and apparatus for controlling the nt Shown in 1, the resistor 00111311865 1 l flf 0 e0 fl t charge currentssummed t0 the different carbon blocks 28 resting on the top of the brdge 3 Cells whereby each 11 is required to take 1 24 which forms theconnection to the posit ve the current necessary for maintaining it inproper terminal of the F shown at line Tight-mild Side condition withoutexcessive overcharge. 05 we of the P Tests a w this Object in View, tprincipa1 fea plate 30 formed on the end a lead caole 32. ture of theinvention comprisesa method and ap- Pressure is a p d the blocks t a ythe c paratus whereby there is supplied to the battery Sistance thereufby an insulating plate 34 engaged a float charge current adequate forthe oldest and by 811 adjustable Screw 35 held in a frame a leastefficient cells and whereby the excess of Cached the bridge The frameqflmpr ses current above that necessary for maintaining the simply all 11 p t 38 ScCllled a ve he bridge newer cells in condition is shuntedaround them. by bolts W i911 are e With insulating 9 Accordingly, eachcell in the battery is required slcevcsfiz to contact OI t e carbonblocks to take only the proper amount of current for thereWlth- The came32 t j h a 001 inaintaining the proper charged condition without 191mg44 With a lead cable Wmcil 1S burned detrimental overcharge. the upperpart of the outermost negative plate of i5 Qther features f t inventioncomprise the cell. It will be seen, thereiore, that a part tain novelmodes of operation and features of the C a ging current which wouldnorma y construction hereinafter described and particufi W f e bridge 24i l t plate an larly defined in the claims. through the electrolyte tothe negative plate is In the accompanying drawing, Fig. 1 is a ec-Toy-passed through the carbon pile and the ca- 50 tional elevation oftwo adjacent cells provided bles 32 and directly to the negative plate,with the preferred form of apparatus according It is occasionallydesirable, ror reasons which to the present invention;: Fig. 2 is adiagram of will hereinafter be made apparent, to determine the batteryand associated control apparatus; and the current diverted by the shuntof any cell. To Fig. 3 is a graph illustrating the method of dethis end,the coupling rnemoer comprises a termining the shunt adjustment. sleevehaving a number or set screws i8 to engage ll;

the ends of the cables 32 and 46. The upper end of the coupling isslotted, as indicated at 50, to permit the uppermost set screw to bepulled out with the cable 32. To measure the shunt current, an ammeteris clipped between one of the lower set screws and the uppermost setscrew, the two upper screws are then loosenedto free them from the cable32, and then the cable is pulled up from the coupling, therebypermitting the ammeter to show a reading. It will be observed that sincethe ammeter is connected prior to separation of the cables, there is nopossibility of an arc on separation of the cables as the circuit remainsclosed through the ammeter, an important factor in a battery room wherethe atmosphere may contain explosive gaseous mixtures.

Although Fig. 2 shows controlling shunts applied only to two of thecells, it will be understood that shunts may be applied to all of thecells, whereby proper adjustment of the charging current may be efiectedfrom the time a cell is put into service until it is finally discarded.It will also be understood that a single shunt may be connected acrosstwo or more adjacent cells of substantially identical characteristics.

The preferred method of arriving at the best adjustments of the shuntswill now be described. It the battery is connected across a source ofsubstantially constant voltage, the procedure is quite simple. It hasbeen found that for any given cell, there is a single best value ofterminal voltage which corresponds to the approximate float current justrequired for maintaining the battery. in condition without overcharge.In the following discussion, it will be assumed that the cells are of atype requiring a terminal voltage of 2.15 volts for new cells having afull charge gravity of 1.210, although, of course, this voltage valuewill vary for cells of difierent manufacture. If a constant potentialdifference of 2.15 volts is maintained across each cell over a longperiod, the float current will at all times be proper for maintainingthe necessary charged condition of the battery. As a cell ages, theoptimum potential difference drops slightly owing to the diminished E.M. F. of the cell, but for a battery having no very old cells, theconstant value of 2.15 volts per cell may be considered the best value.With the constant bus voltage, the number of cells in service isadjusted so that the bus voltage divided by the number of cells is asnearly as possible 2.15

volts per cell. .The shunts of the newercells are then adjusted todivert a suflicient amount ,or current so that the terminal voltage oneach'of such newer cells is approximately 2.15 volts. Although the totalfloat current may, in a given instance, be, say, 50 amperes, the netfloat current through a new cell may be between 20 and 30 ampores, whichis sufficient for such a cell because of its smaller local action.

If the shunts of the present invention were not applied, the same floatcurrent would flow through all cells and the terminal voltage of thenewer cells might be as high as 2.25 volts, indicating excessive floatcurrent and consequent destructive action on the cell.

On a bus with a fluctuation voltage, the problem of arriving at thecorrect adjustment is somewhat more difiioult. Even with the balancingeffect of the end cells, a fluctuation of several hudredths of a voltper cell can easily oc-' cur. In such a case, it is necessary to adjustfor the average over a period and by a series of empirical checks toarrive at the shunt setting which most nearly givl s the requiredaverage float current to maintain the cell in proper condition.According to this procedure, curves are charted showing variations ofbus voltage and variations of cell voltage with-respect to time. Suchcurves are shown in Fig. 3 with points taken at approximately half hourintervals. This bus voltage is plotted in full lines as volts per cell,namely, the total bus voltage divided by the number of cells in serviceat the time of measurement. In dotted lines is plotted a typicalterminal voltage graph of a new cell yvith approximately the propershunt adjustment. It will be noted that the time during which theterminal voltage of the cell is in excess of 2.15 is at least partiallycompensated by a voltage less than 2.15 for another part of theinterval. If the actual plotted graph of cell voltage were higher thanthat indicated, the-shunt would be set to divert more current andthereby to lower the curve somewhat.

In adjusting by the average method above described, it is sufficient, asa practical matter, to

'set the shunt so that the cell voltage curve does not vary greatly fromthe bus voltage curve. A

more exact average can be ,found by integrating the curves but this isin practice an unnecthe proper value because there is not a straightline relation between current and terminal voltage. For these reasons,it will be seen that nicety of adjustment is not essential, it beingnecessary only to adjust for an approximate average of cell voltage onthe newer cells, as indicated by Fig. 3. It will be appreciated that aslight excess of float current is not harmiul'except as it contributesto the ageing of the cell; a deficiency, however, will result in failureto keep the cell charged, but such deficiency is quickly reflected inalowering of terminal voltage and can be detected if occasional checkgraphs are made.

The provision for current measurement through the separable coupling 44affords a means of efiecting a quick tentative adjustment of the shunt.For example, when a new cell is cut into service, experience may showthat the required average float current for cells of similar manufactureis in the neighborhood of .30 amperes, as contrasted with 50 amperes forthe older cells. Immediately after installation, the shunt may beadjusted to indicate a diverted current of 20 amperes. Subsequent moreexact adjustments may be made by comparative voltage graphs of the typeshown in Fig. 3. Thereafter, occasional check graphs may be made todetermine whether the fioat current is proper for maintaining the cellin condition.

It will be seen that any shunt diverts a substantially constant current,the shunt current being proportianal to the terminal voltage of the cellwhich, in normal operation, does not vary more than a few hundredths ofa' volt. The actual float current through a shunted cell, however,varies considerably with a slight change of voltage. If desired, theactual float current change is necessary between summer and winter,

if the temperature of the battery room varies widely; For examplefinwinter, the average float current for an old cell may be in theneighbori' hood of 50 amperes and the desired cur: ent for a new cell inthe neighborhood of 20 anperesf In summer, the local action increasesconsiderably so that the total float current taken by the battery mayrise to 100 amperes, the terminal voltages remaining approximately thesame. Since the shunt on the new cell diverts a substantially constantcurrent (30 amperes in the examplc given), it will be seen that the newcells would take a float current far in excess of their requirements.Some tightening of the shunts is therefore necessary to divert a greaterproportion of the current. The readjustment of the shunts is determinedby preparing new.graphs of the type indicated in Fig. 3, Furthermore,some adjustment from time to time is obviously necessary as the cellsbecome older, to increase the float current and thereby to compensatefor the naturally increased local action. Such changes in thcadjustments of the shunts to meet changed conditions are equallynecessary for a battery which is connected to'a constant voltage and fora battery connected to a fluctuating bus. In any event, the proper shuntadjustments may be maintained with sufflcient accuracy by periodiccomparisons of cell voltage with the bus voltage, as illustrated by thegraph of Fig. 3.

The shunts have no appreciable effect on the battery during discharge. Acell of the size referred to may discharge, under emergency conditions,at a rate of several thousand amperes, and the small current diverted byany of the shunts is of no consequence. Similarly, if the battery ischarged at a high rate, as is necessary after a discharge, theproportion of current taken by the shunts is negligible.

It will be seen that although the energy taken by the shunts duringnormal floating is wasted, such' energy would also be wasted if passedthrough the cells and would furthermore have a positively detrimentalaction on the cells.

Although the preferred embodiment of the present invention has beendescribed, the invention is not limited to such preferred embodiment,but may be varied within the scope of the appended claims.

Having thus described the invention, what is claimed is:'

.1. The method of controlling the float charge of storage battery cellsof different ages and conditions and series connected across a supplyline which consists in supplying a float charge current sufficient tomaintain the oldest cells in charged condition, and shunting around thenewer cells an excess of current above that necessary to maintain saidcells in proper charged condition.

2. The method of controlling the float charge of storage battery cellsof different ages and conditions and series connected across a supplyline which consists in supplying a float charge current suflicient tomaintain the oldest cells in charged condition. and shunting sufficientcurrent around the newer cells to diminish the terminal voltages of suchcells to values approxi mating the terminal voltages of the older cells.

3. The method of controlling the float charge of storage battery cellsof different ages and con- I ditions and series connected across asupply line which consists in supplying a float charge currentsufficient to maintain the oldest cells in charged condition, andshunting sufficient cur rent around the newer cells to prevent passagethrough said cells of current greatly in excess of that required tomaintain the cells in charged condition.

4. The method of controlling the float charge of storage battery cellsof different ages and conditions and series connected across a supplyline which consists in supplying a float charge current sufficient tomaintain the oldest cells in charged condition, and shunting eachof thenewer cells with a substantially constant resistance to limit thecurrent through said cells.

5. The method of controlling the float charge of storage battery cellsof different ages and conditions and series connected across a supplyline of fluctuating voltage which consists in'supplying a float chargecurrent sufficient for the older cells, and shunting current around thenewer cells to maintain the average terminal voltage of said cells at avalue approximately corresponding to that voltage most satisfactory forfloat, charging without excessive overcharge.

6. The method of controlling the float charge of storage battery cellsof different ages and conditions and series connected across a supplyline of fluctuating voltage which consists in supplying a float chargecurrent sufficient for the older cells, and shunting around the newercells a substantially constant current sufficient to maintain theaverage terminal voltages of such cells at values not excessivelygreater than the average value of the supply voltage per cell.

'7. A float battery system comprising a bus, a battery of seriesconnected cells floating on the bus, the cells being of different agesand conditions, and shunts connected around less than all of the cellsto divert float current therefrom.

8. A float battery system comprising a bus, a battery of seriesconnected cells floating on the bus, the cells being of different agesand conditions, and adjustable carbon pile resistors connected aroundnewer and more efficient cells to divert a part of 'the float currenttherefrom.

9. A float battery system comprising a bus, a. battery of seriesconnected cells floating on the bus, the cells being of different agesand conditions, bridges connecting plates of adjacent cells to form theseries connections therefor, a pile of carbon resistance blocks on atleast one of the bridges, a frame for supporting the blocks, and a cableconnection from the top of the pile to a battery plate of polarityopposite to that to which the bridge is connected.

10. A float battery system comprising a bus, a battery of seriesconnected cells floating on the bus, the cells being of different agesand conditions, a shunt for at least one of the cells, a connection fromthe shunt to one side of the cell including two cables, a separablecoupling member for the cables, and means for connecting a meter betweenthe cables prior to separation thereof.

11. A float battery system comprising a bus,

set screws connecting the sleeve to the cables,

the sleeve having a slot to permit disengagement of one of the screwstherefrom when one of the vof the current above that cables is pulledfrom the sleeve, the screws serving as terminals to which angammeter maybe attached.

12. The method oi controlling the float charge of series connectedstorage battery cells or ditierent conditions which consists insupplying a total float charge current sufiicient to maintain incondition those cells requiring the maximum charge, and shunting aroundthose cells of storage battery cells of diflerent conditions and seriesconnected across a supply of fluctuating voltage which consists insupplying a float charge current sufllcient for those cells requiringthemaximum charge, and shunting around the more eflicient cellssufiicient current to maintainthe average terminal voltage across allcells at approximately the same value.

15. The method of controlling the float charge '0! storage battery cellsof different conditions and series connected across a supply offluctuating voltage which consists in supplying a float charge currentsuflicient for those cells requin'ng the maximum charge, and shuntingaround the more eiflcient cells sufiicient current to maintain theaverage terminal voltage of said cells at 'approximately'the valuecorresponding to the optimum voltage for float charging withoutexcessive overcharge;

16. A float battery system comprising a bus, 8. battery ofseries-connected cells floating on the bus, the cells being of difierentages and conditions, and individual shunts connected around the moreeflicient cells to divert float current therefrom.

OSCAR B. Benson.

